Today, a traditional drain valve assembly is mounted in the drain of a sink using a top pipe with an annular collar flange and a main drain pipe, connected by screw thread to each other and connected to the sink by applying the collar flange of the top pipe to the top side of the sink as the collar flange has a larger diameter than the drain opening. The interface between the flange and the sink has to be sealed with a sealant or a putty to secure that the interface is water-proof. Beneath the sink, the main drain pipe is connected to the top pipe through the drain of the sink. The interface between a flange of the main drain pipe and the underside of the sink also has to be sealed to secure that the interface is water-proof.
However, the interface between the annular collar flange of the top pipe and the top side of the sink is difficult to seal completely, and further, this interface is difficult to clean. Deposits, such as dirt, are continuously accumulating at this interface. Further, it is difficult to install traditional pop-up drain valve assemblies, because a pivoting lever has to be installed parallel to the front of the sink and adjustments are often needed to correct the installation of the pivoting lever.